1. Field of the Invention
The present invention relates to an optical system for changing the shape of a light beam. More particularly, the present invention relates to an optical system for shaping a light beam in a semiconductor laser, etc. used in a pickup for an optical disk.
2. Description of the Related Art
In general, semiconductor lasers have aspect ratios different from each other in their light emitting regions. Accordingly, it is indispensable to dispose a beam shaping optical system when a circular light spot is formed on the optical disk.
However, the general beam shaping optical system using a prism has the following disadvantages.
(1) It is difficult to adjust an optical path in the optical system since an optical path is bent by the prism.
(2) When a light beam provided by a joining lens is slightly shifted from a collimated light beam, astigmatism is caused by the prism. Therefore, asymmetric aberration is caused with respect to a light spot converged by a condenser lens.
(3) When ratios of divergent angles of light beams emitted in directions perpendicular to each other are greatly different from each other every semiconductor laser, it is necessary to replace the prism by another prism and change an incident angle of the laser beam incident to the prism. Therefore, it is necessary to adjust the operation of the entire optical system again.